Some databases use timestamp-based multi-version concurrency control (MVCC) to minimize conflicts with regard to simultaneous transactions. With this arrangement, records in the database are (logically) tagged with creation and deletion timestamps that correspond to transactions that created and deleted the record. If a record has not yet been deleted, the deletion timestamp is unset (which can be represented by some special value, such as maximum representable integer value).
A consistent view (or snapshot) on the database is needed to ensure consistent execution of a SQL statement or of a whole transaction. The consistent view is created by taking the current value of the commit timestamp generator. This timestamp is then used against create and delete timestamps (CTS, DTS) to decide visibility of the record.